Both waves and currents rank highly by user groups among oceanographic observation variables. Real-time information of these variables is especially useful for vessel operators and recreational users in and around ports, harbors and bays. Other applications include coastal land management, ecosystem protection and restoration, mitigation of coast hazards and marine accidents, forecast, warning and search and rescue. The U.S. National Ocean Service (NOS) of NOAA maintains and operates a Physical Oceanography Real-Time System (PORTS®) in the Nation's major ports and harbors. Typical hydrological parameters measured include water levels, currents, conductivity, water temperature and depth. Wave information is of interest to PORTS® users, but has only been obtained recently in a few PORTS® sites. However, continued study and laboratory and field testing of various wave measurement instruments and real-time data telemetry technologies have been conducted since 2003. These instruments and technologies include Triaxys Directional Wave buoy, Directional Waverider buoy, and acoustic Doppler current profilers, underwater acoustic modem and links with radio and satellite. Extraction of non-directional wave information from near shore tide gauges (e.g., air acoustic gage and microwave radar altimeter) has also been studied. Among these, acoustic Doppler current profilers (or ADCP) are of particular interest since they are key instrument in PORTS® for current measurements. It is economically and functionally attractive to measure both currents and waves. This paper summarizes the NOS operational system and results of two NOS field studies of real-time ADCP systems for current and wave measurements in ports and harbors. The operational system includes bottom-mounted ADCP with buried cable in the navigation channel. Later, the system was replaced by a U.S. Coast Guard Aid-to-Navigation (ATON) buoy-mounted ADCP with telemetry radio. Shore based Horizontal ADCPs are also being used for real-time current measurement. The two studies (in 2003 and 2008) used different ADCP instruments and data telemetry techniques. The ADCPs used were RDI Workhorse series and AWAC (with internal processor). The underwater acoustic modems used were models UWM1000 and UWM2000H by LinkQuest. The data telemetry technologies used were FreeWave 900MHz spread spectrum line-of-sight radios, and Iridium satellite.

Real-time current and wave measurements in ports and harbors using ADCP

The U.S. National Ocean Service (NOS) of NOAA maintains and operates a Physical Oceanography Real Time System (PORTS®) in the Nation’s major ports, harbors and bays. The traditional method of obtaining real-time data from bottom mounted instruments is via underwater cable link. However, this is vulnerable to damage and costly to install and maintain. This paper describes an approach utilizing acoustic and Iridium satellite links to report in real-time wave and current data. The system consists of an ocean bottom instrumentation platform and a U.S. Coast Guard Aid-to-Navigation buoy for data relay. The bottom platform contains a Nortek 1 MHz Acoustic Wave and Current profiler (AWAC) with an integrated Nortek Internal Processor (NIP), a LinkQuest omni-directional UWM2000H underwater acoustic transmitting modem, an ORE acoustic release-based recovery component, and a Teledyne-Benthos UAT-376/EL acoustic transponder. The surface buoy supports an omni-directional UWM2000H receiving modem, an Iridium antenna, and an electronic box containing an Iridium modem, a controller, battery packs, and temperature and voltage sensors. The AWAC measures current profiles along the vertical water column at 30-minute intervals and surface waves at hourly intervals. The NIP processes a set of user selected wave and current parameters and sends these data to the controller on the surface buoy through acoustic modems. The data are then transmitted via Iridium satellite to remote offices in real-time. Sample measurement results and reference data from a near-by Datawell’s Waverider directional wave buoy are presented. The Waverider is operated by the U.S. Army Corps of Engineers (USACE) and Scripps Institution of Oceanography (SIO). Several unique system design features and interesting wave phenomenon observed at the measurement site are discussed. The goal of this project is to demonstrate the performance of AWAC, NIP, shallow water acoustic modems, and Iridium satellite in real-time data telemetry.

John Cassidy

Papers

Real-Time Current and Wave Monitoring Using Acoustic and Iridium Satellite Links